1. Field of the Invention
The present invention relates to a stamper used when manufacturing an information recording medium, an imprinting method that presses a stamper into a resin layer formed on a surface of a substrate to transfer a concave/convex form of the stamper, and a method of manufacturing an information recording medium using a concave/convex pattern transferred to a resin layer.
2. Description of the Related Art
Optical lithography is conventionally known as a method of forming a fine concave/convex pattern (a resist pattern) in a resist layer (a resin layer) formed on a surface of a substrate during a process that manufactures an information recording medium or the like. When optical lithography is carried out, a resist layer formed on a substrate is irradiated with light to form an exposure pattern and then the resist layer is developed to form a concave/convex pattern on the substrate. In recent years, electron-beam lithography that draws a pattern of nanometer size using an electron beam instead of light to form a concave/convex pattern has been developed as a technique for forming an even finer pattern. However, electron-beam lithography has a problem in that a long time is required to draw a pattern on the resist layer, making such technique unsuited to mass production.
As a method of solving this problem, U.S. Pat. No. 5,772,905 discloses a nano-imprint lithography method (i.e., an imprinting method that forms a concave/convex pattern of nanometer size: hereinafter simply “imprinting method”) that forms a concave/convex pattern of nanometer size on the substrate by pressing a stamper on which a concave/convex pattern of nanometer size has been formed onto a resin layer on a substrate to transfer the concave/convex form of the stamper to the resin layer. With this imprinting method, first as shown in FIG. 1A of U.S. Pat. No. 5,772,905, a stamper (“mold”) 10z (hereinafter component elements disclosed in the specification of the USP are indicated by reference numerals appended with “z”) that has a concave/convex pattern of nanometer size (as one example, with a minimum width of around 25 nm) formed in a transfer surface thereof is manufactured. More specifically, an electron beam lithography apparatus is used to draw a desired pattern on a resin layer formed so as to cover a thin film (“molding layer”) 14z made of silicon oxide or the like that has been formed on the surface of a silicon substrate 12z, and then the thin film 14z is etched by a reactive ion etching apparatus with the resin layer as a mask to form a concave/convex pattern with a plurality of convex parts (features) 16z within the thickness of the thin film 14z. By doing so, the stamper 10z is manufactured.
Next, as one example, polymethyl methacrylate (PMMA) is spin coated on the surface of a silicon substrate 18z to form a resin layer (a “thin film layer”) 20z with a thickness of around 55 nm. Next, after heating both the stamper 10z and a multilayer structure composed of the substrate 18z and the resin layer 20z to around 200° C., as shown in FIG. 1B of the U.S. Pat. No. 5,772,905, the convex parts 16z of the stamper 10z are pressed into the resin layer 20z on the substrate 18z with a pressure of 13.1 MPa (133.6 kgf/cm2). After this, the multilayer structure is left to cool to roam temperature in a state where the stamper 10z is still pressed in (i.e., a cooling process is carried out), and then the stamper 10z is separated from the resin layer 20z. By doing so, as shown in FIG. 1C of the U.S. Pat. No. 5,772,905, the convex parts 16z of the concave/convex pattern of the stamper 10z are transferred to the resin layer 20z to form a plurality of concave parts (“regions”) 24z, thereby forming a concave/convex pattern of nanometer size (in the resin layer 20z) on the substrate 18z. 